It's all about the chromosomes (and mitochondria) The 23 chromosomes of a human male . Courtesy: National Human Genome Research Institute X, Y and Mitochondrial DNA are less well-known and not used by many genealogical researchers. Both Y and MtDNA tests are more expensive than the more common autosomal DNA tests.  X is always tested in an autosomal DNA test. However X results are less reported (FTDNA, 23andMe) or not reported at all (Ancestry, MyHeritage, LivingDNA), with the exception of Gedmatch. Rather than covering generations of your ancestry, each of these DNA types cover a smaller portion of your tree, which some see as a weakness.  However, because of that restriction, the researcher gets a focused result, which can be powerful, if the test will help you answer your research question.  Y DNA tests were first offered to the consumer in 2000 by only one company: FamilyTreeDNA. Ancestry also offered Y and mitochondrial tests between 2012 and 2014...